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Recovering from Vortex Ring State - The Vuichard Technique

April 3, 2018

30 years ago, while flying an AS350 Squirrel over mountainous terrain in Switzerland, carrying a log on a 40-metre rope, helicopter pilot Claude Vuichard and his instructor got caught in an updraft, causing them to enter a vortex ring state, and found themselves sinking rapidly. They regained control just metres from the tree tops. A shaken Claude returned home convinced that there must be a better way to recover from vortex ring state.

 

 

 

Vortex ring state occurs when the helicopter descends into its own downwash, causing severe loss of lift. instinctually the pilot would feel the increased rate of descent (ROD) and attempt to overcome this by raising the collective to increase the Rotor Thrust. The net result is an increased ROD due to the further development of the Vortex Ring State. There is the sense that the collective is no longer connected – you apply collective and continue to sink rapidly.

How does it form? In forward flight, there is no upward flow (upflow) of air in the hub area. During a hover or descent, the volume of upflow increases, and the induced flow (air pulled down through the rotor system) of the inner blade sections is overcome. The blades begin to stall near the hub, decreasing the amount of lift being produced and resulting in an increase in sink rate. In other words, the onset of upward (or ROD airflow) around the main-rotor hub and blade root sections (non-lifting producing areas) during high vertical descent rates causes the blades to rapidly stall from the root outwards. In this state, the helicopter is operating in its own downwash, descending through descending air at over 3,000 ft per minute. The only option to stop sinking is to get out of the turbulent air.

Because helicopters generally fly at around 500 ft AGL, if you enter a vortex ring state, you don’t have much time before you hit the ground. In more powerful helicopters, with high disk loads, the rate of descent will be far higher, and so there is even less time to recover.

Claude Vuichard reckons the traditional recovery method from vortex ring state was carried over from the recovery from a stall in aeroplanes – lowering the nose – as many early helicopter pilots initially flew fixed-wings. So, when caught in vortex ring state, helicopter pilots were taught to move the cyclic forward, reduce power to reduce induced drag and the resultant vortices, and then only raise collective to add power once you had recovered. While this works, provided you are not in a tailwind, it often results in a significant loss of altitude – 500 ft. And because it generally occurs near the ground, that’s not an option. So, pilots are simply taught how to avoid the situation. Just as spin recovery is not a certification requirement in fixed-wings, so recovery from vortex ring state is not required for certification of helicopters.

Claude was determined to develop a recovery method that wouldn’t result in such a loss of height. After his close call over mountains, he spent days meticulously going through the physics, and then confidently climbed into his helicopter to test the theory. Sure enough, having set up a sink in a vortex ring state, he recovered in less than 50 ft.

 

THE VUICHARD RECOVERY TECHNIQUE

Claude suspected that reducing height loss would require catching the upwind part of the vortex being pulled around the ends of the rotor blades with the advancing blade. This is best done by flying sideways out of the turbulent air by using cyclic to bank 15-20 degrees in the direction of tailrotor thrust. At the same time, to further reduce height loss, takeoff power is set and the torque increase of the main rotor is compensated with the power pedal to maintain heading.

In helicopters with counter-clockwise rotating main rotors, the torque which causes the nose to go to the right that comes with an increase in power is compensated with left pedal. Left pedal also prevents the helicopter from weather-cocking as you move sideways. Thus, direction of thrust from the tailrotor is to the right, in the direction you want to move, and the bank to get lateral movement to exit the vortex ring state would be to the right, resulting in a cross-control situation.

As soon as the rotor reaches the upwind part of the vortex, outside the rotor tips, the recovery is completed with a return to straight and level flight. Average reported height loss is 20-50 ft – 10 times less than with the traditional method.

An added advantage of the Vuichard Recovery Technique is that it fits in with early training and the instinctual response to counteract a descent – raising collective. The traditional method conflicts with this instinct – known as primacy. You have to use reason to overcome your initial reaction, and there is no time for that. This primacy is also why Claude suggests recovery from vortex ring state be taught early in training – as soon as you can hover. When you start flight training you are pumped up on adrenaline, and this is when taught behaviour firmly entrenches itself in your brain. When you are under stress and your adrenaline kicks in during an emergency, you brain will revert to what it learned when it was initially in that state. “The emotion drives the motion,” says Claude. You want the instinctual response to be raised collective, and lateral movement in the opposite direction of the power pedal.

 

ADOPTION OF THE TECHNIQUE

In 2011 Claude demonstrated his technique to Tim Tucker, Robinson Helicopters’ Chief Instructor, in Switzerland. Tim was impressed. “Suddenly he woke up from his jet-lag,” Claude says with a grin.

Tim took this new recovery technique back to the States, and started demonstrating it to other instructors, test pilots and operators – such as the US Coast Guard. Everyone agreed that it worked better than the traditional method. It took three years, but in 2014, Robinson began teaching the Vuichard Recovery Technique at all its safety courses, and implemented it into their ‘Flight Training Guide’.

The spinoff is that it is starting to gain traction worldwide in younger pilots, as Robinson R22s and R44s are still the staple helicopter trainers. Large operators too, such as Air Methods, the biggest medical transport company in the US, as well as the Los Angeles Police Department, have adopted it as their stipulated recovery method.

Helicopter Association International (HAI) awarded Claude Vuichard HAI’s Salute to Excellence BLR Aerospace Safety Award for 2018.

Yet, despite this recognition, and although demonstrations continuously prove that the technique works, adoption is slower than Vuichard would like, largely because instructors will teach what they have been taught, and revert to initial training when under stress. Thus, old procedures are conserved.

Another challenge is that teaching the Vuichard Recovery Technique in simulators would require reprogramming simulators worldwide, as the algorithms currently do not accept the method.

 

A NOBLE VISION

In 2015, Claude set up a non-profit organisation, the Vuichard Recovery Aviation Safety Foundation, with the goal of reducing vortex ring state related accidents to zero, and the overall helicopter accident rate by 80 percent. A year later, he took early retirement from the Federal Office of Civil Aviation in Switzerland to conduct safety courses worldwide.

He believes that correct training is the solution to aviation accidents. “Accidents are always the same; all that changes are the dates and registrations. The problem is between the headset,” says Claude. Regulations are written as a reaction to accidents, or to prevent them, but “increased regulation won’t improve safety”.

Over time, regulations have swollen to thousands of pages, “but they have missed the target, because we are flying less and having more accidents. We are producing accidents through regulation,” says Claude.

In his efforts to curb accidents through training, Claude has developed a range of techniques that deal with all typical accident types, such as dynamic rollover, engine failure and auto-rotation, slope landings and quick stop techniques. Thanks to the growing acceptance of his vortex ring state recovery technique, pilots are becoming more receptive to his methods. However, some manufacturers are showing resistance due to the process and costs of recertification. Interestingly, the vortex ring state recovery method isn’t being resisted because it isn’t required for certification, says Claude.

In October last year, Claude toured SA, but was frustrated by the turn out. He held three courses, advertised by the CAA, in Johannesburg, one in Durban and one in Cape Town. In total, only around 65 pilots attended the courses. Helicopter pilot and instructor, Nick Cook says, “We have a disaster looming in our industry – I have been watching this for years. Operators do not like spending money on training. To quote Mike Litson when I worked with him at Court Helicopters 20 years ago, he used to say to Jeremy Labuschagne, ‘If you think training is expensive, try an accident.’ I see it wherever I go – people do not like spending money on training.”

What was encouraging, however, was that most were commercial pilots and instructors, who are likely to pass on the training to other pilots. And their responses were hugely positive. The big disappointment was that no-one from the military or police showed up.

Claude draws no salary from his safety seminars and courses, and travels the world in an honest effort to improve aviation safety, and the helicopter community is starting to pay attention. To find out more about his recovery techniques, visit the Vuichard Recovery Aviation Safety Foundation website www.vrasf.org. There you will find demonstration videos, Powerpoint presentations and articles.

 

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